Summary Increasing the levels of anti-inflammatory lipid mediators could be one mechanism to promote the res- olution of inflammation. Specialized pro-resolving lipid mediators (SPMs), such as lipoxins and re- solvins, have been extensively characterized, whereas lipid glyceryl esters, such as 2-arachdi- onoylglycerol (2-AG) and prostaglandin glyceryl esters (PG-Gs), are emerging as potential SPMs but much remains unknown about these compounds. Carboxylesterases (human and mouse gene symbols are CES and Ces, respectively) are enzymes and members of the serine hydrolase (SH) superfamily. Ces enzymes are widely distributed in mice and global Ces3 knockout mice are available. Ces3 is one of the most abundant Ces isoforms in mice, and, of all Ces isoforms, it has the highest sequence ho- mology to human CES1. CES1 and Ces3 both metabolize and degrade 2-AG and PG-Gs, suggesting that inactivating their activity with small molecules might augment the levels of these lipid mediators in the setting of inflammation and promote resolution. A recent study from our group indicated that sys- temic inflammation in mice (induced by LPS treatment) caused 2-AG hydrolytic activity to be downreg- ulated in spleen, which we infer will increase the local concentration of this endocannabinoid. 2-AG per se often exhibits anti-inflammatory effects, whereas its hydrolytic and oxidative catabolism produces pro-inflammatory arachidonic acid and PGE2-G, respectively. This suggests that inhibition of 2-AG me- tabolism might be one negative feedback mechanism to resolve inflammation. We hypothesize that inflammation downregulates CES activity in tissues to promote resolution (and restore homeostasis) and that CES is a novel anti-inflammatory target to reverse pathology associated with inflammatory disease. 3 specific aims will test this idea: SA1: Using an animal model of systemic inflammation, es- tablish whether pharmacological inactivation of Ces3 by WWL229, or global Ces3 knockout, reverses the associated inflammation and improves disease outcome. SA2: Characterize the serine hydrolase profile and endocannabinoid-eicosanoid crosstalk in a mouse model following endotoxin challenge. SA3: Elucidate the molecular and cellular mechanisms that regulate CES activity within macrophages. If the proposed studies are successful and this hypothesis is borne out, it will provide the impetus to develop more potent and isoform-selective inhibitors for CES to treat inflammatory disease in a variety of contexts, including autoimmune disease, atherosclerosis, and metabolic diseases.